/* This is free and unencumbered software released into the public domain. */
#include <stddef.h>
#if defined(__x86_64__) && defined(__POPCNT__)
#  include <nmmintrin.h>
#endif

/* Append data to a CRC-32C checksum. Use 0 for the initial checksum.
 */
static unsigned long
crc32c_update(unsigned long crc, const void *buf, size_t len)
{
#if defined(__x86_64__) && defined(__POPCNT__)
    /* No feature macro for _mm_crc32_u64, use __POPCNT__ as a proxy. */
    size_t ntail = len % 8;
    size_t nblocks = len / 8;
    const unsigned long long *blocks = buf;
    const unsigned char *tail = (const unsigned char *)(blocks + nblocks);
    crc ^= 0xffffffff;
    for (size_t i = 0; i < nblocks; i++)
        crc = _mm_crc32_u64(crc, blocks[i]);
    for (size_t i = 0; i < ntail; i++)
        crc = _mm_crc32_u8(crc, tail[i]);
    return crc ^ 0xffffffff;
#else
    static const unsigned long crc32c_table[] = {
        0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f,
        0x35f1141c, 0x26a1e7e8, 0xd4ca64eb, 0x8ad958cf, 0x78b2dbcc,
        0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3, 0xac78bf27,
        0x5e133c24, 0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b,
        0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384, 0x9a879fa0,
        0x68ec1ca3, 0x7bbcef57, 0x89d76c54, 0x5d1d08bf, 0xaf768bbc,
        0xbc267848, 0x4e4dfb4b, 0x20bd8ede, 0xd2d60ddd, 0xc186fe29,
        0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
        0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5, 0x6dfe410e,
        0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa, 0x30e349b1, 0xc288cab2,
        0xd1d83946, 0x23b3ba45, 0xf779deae, 0x05125dad, 0x1642ae59,
        0xe4292d5a, 0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a,
        0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595, 0x417b1dbc,
        0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0,
        0x67dafa54, 0x95b17957, 0xcba24573, 0x39c9c670, 0x2a993584,
        0xd8f2b687, 0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
        0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927, 0x96bf4dcc,
        0x64d4cecf, 0x77843d3b, 0x85efbe38, 0xdbfc821c, 0x2997011f,
        0x3ac7f2eb, 0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4,
        0x0f36e6f7, 0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096,
        0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789, 0xeb1fcbad,
        0x197448ae, 0x0a24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1,
        0xcdbe2c45, 0x3fd5af46, 0x7198540d, 0x83f3d70e, 0x90a324fa,
        0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6,
        0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd,
        0xceb018de, 0xdde0eb2a, 0x2f8b6829, 0x82f63b78, 0x709db87b,
        0x63cd4b8f, 0x91a6c88c, 0x456cac67, 0xb7072f64, 0xa457dc90,
        0x563c5f93, 0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043,
        0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c, 0x92a8fc17,
        0x60c37f14, 0x73938ce0, 0x81f80fe3, 0x55326b08, 0xa759e80b,
        0xb4091bff, 0x466298fc, 0x1871a4d8, 0xea1a27db, 0xf94ad42f,
        0x0b21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033,
        0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9,
        0x97baa1ba, 0x84ea524e, 0x7681d14d, 0x2892ed69, 0xdaf96e6a,
        0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0x0e330a81,
        0xfc588982, 0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d,
        0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622, 0x38cc2a06,
        0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19, 0x0d3d3e1a,
        0x1e6dcdee, 0xec064eed, 0xc38d26c4, 0x31e6a5c7, 0x22b65633,
        0xd0ddd530, 0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f,
        0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff, 0x8ecee914,
        0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0, 0xd3d3e1ab, 0x21b862a8,
        0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643,
        0x07198540, 0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90,
        0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f, 0xe330a81a,
        0x115b2b19, 0x020bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06,
        0xc5914ff2, 0x37faccf1, 0x69e9f0d5, 0x9b8273d6, 0x88d28022,
        0x7ab90321, 0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e,
        0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a,
        0xc69f7b69, 0xd5cf889d, 0x27a40b9e, 0x79b737ba, 0x8bdcb4b9,
        0x988c474d, 0x6ae7c44e, 0xbe2da0a5, 0x4c4623a6, 0x5f16d052,
        0xad7d5351
    };
    size_t n;
    const unsigned char *p = buf;
    crc ^= 0xffffffff;
    for (n = 0; n < len; n++)
        crc = crc32c_table[(crc ^ p[n]) & 0xff] ^ (crc >> 8);
    return crc ^ 0xffffffff;
#endif
}
